US2628458A

US2628458A - Gear grinding machine

Info

Publication number: US2628458A
Application number: US155157A
Authority: US
Inventors: Buhler Hermann
Original assignee: Maag Zahnrader und Maschinen AG
Current assignee: Maag Zahnrader und Maschinen AG
Priority date: 1950-02-18
Filing date: 1950-04-11
Publication date: 1953-02-17
Anticipated expiration: 1970-02-17

Description

Feb. 17, 1953 H. BUHLER 2,628,458

' GEAR GRINDING MACHINE Filed April 11, 1956 4 sheets-sheet 1 Feb. 17, 1953 l ..BUHLER f 2,628,458

' GEAR GRINDING MACHINE 4 Sheets-Sheet 2 Filed April l1, 1950 4 Sheets-Sheet 3 WWW H. BHLER GEAR GRINDING MACHINE Feb. 17, 1953 Filed April 11, 195o Feb. 17, 1953 H. BUHLER 2,628,458

" GEAR GRINDING MACHINE Filed April 11, 195o -4 sheets-sheet 4 @me/:5% 27% Y Patented Feb. 17, 1953 UNITED STATES rm" oFFlcE GEAR GRINDNG MACHINE Application April 11, 1950, Serial No. 155,157 'In Switzerland February 18, 1950 9 Claims.

This invention relates to gear grinding machines operating on the involute-generating princip'le'in'which the Work andthe grinding tool are caused to move relatively to each other with a true rolling motion so that the Working surface of the tool describes an involute surface enveloping the flank of the gear tooth to be ground.

Itis usual for this rolling motion to be brought about by a member having a cylindrical surface or a surface which iS part of a cylinder of diameter corresponding to the base circle diameter of, and mounted coaxially with, the gear wheel to be ground, the cylindrical surface being connected to V:flexible steel tapes under tension which ensure a relative rolling motion without slipping between themselves and said member (which is hereinafter referred to as the involute-generating cylinder) In one known type of such gear grinding machines, the involute-generating cylinder and the work are connected together and mounted for joint rotation and for bodily rectilinear reciprocation perpendicularly to their joint axis, while the other ends of the steel tapes are fastened to a member which in operation remains stationary, the reciprocation of the involute-generating cylinder relatively to the tapes causing the involute-generating cylinder and the work to rotate in an oscillatory manner so that the combined rotary and reciprocating movements thereof, while the tapes are beingwound on and unwound from the involute-generating cylinder, represent a true rolling motionof the work with respect tothe grinding tool which is also stationary in space during normal operation.V

In another known type of such grinding machines, the involute-generating cylinder and the work remain stationary during operation (except for periodical rotation of the work for dividing or indexing purposes, i. e. in order to present different gear teeth successively tothe tool) and it is thevtool which performs the true rolling motion relatively to the work, which motion is composed of a combined rotary and rectilinear reciprocating movement of the tool and its holder,

the latter being mounted for rotation about the joint axis of the involute-generating cylinder and the work and for reciprocation perpendicularly to said axis, the rotary component being in the nature of an oscillation imparted to the tool-holder which is connected by the steel tapes to the in- The present invention relates only to this latv 2 ter type of gear grinding 'machine and has for object to provide improvements therein. e i

According to the invention the driving means' for imparting the. rotary compo-nent of 'movement to the tool-holder comprises a power-driven shaft mounted parallel to the axis of the involutegenerating cylinder in fixed. relation to the inachine bed, a screw-threaded spindledriven by said shaft and engaging a nut pivotally con-- nected to the tool-holder, and means between said shaft and the tool-holder adapted to permit said rotary movement of the tool-holder 'relatively to said shaft notwithstandingvthedrivng connection therebetween by said spindle and said nut. o c

The said means may ktake the form of pivotal means enabling said spindle to pivot aboutfan axis provided by said shaft, `so that in operation said spindle swings towards and away from the tool-holder. For example, said spindle may be driven through a pair of bevel wheels secured to said spindle and to said shaft respectively, said shaft having mounted for pivotal: movement thereon a member which provides lthe bearingffor said spindle and its bevel wheel. of said spindle may be slidably supported.

Alternatively said means may provide forfsaid nut to have a movementtowards and away from the tool-holder, in addition .to its pivotal connection thereto, while said spindle has no bodily movement relatively to the machine bed. For example, the pivot of said nut may be slidable in a guide of the tool-holder, or it mayv be pivoted to the end of a lever adapted to swing towards and away from the tool-holder. i

A machine embodying the invention may also haveA provision for controlling the aforemenltioned driving means so vas to reverse vthe rotary movement of the tool-holder every time it reaches the end o f a prede'ztermined arc of rotation through which it is to oscillate, ,For this 'purr pose, use is preferably made of the drive of .said shaft to operate a trip mechanism which causes the rotation of -said, spindleto b reversed.

In one embodiment of the invention, the toolfholder comprises an upright standard, upon which one or more grinding wheels are adjustably and reciprocably mounted, and a table Indunted for pivotal movement about thev axisolf lthe invollitelr generating cylinder, the standard being inoun d on the table so as to be adjustable towardsj'and away from the work, and, in` addition, slidable with rrespect to the table tangentially' of th i111-v volute-generating cylinder for the'purposerof `perf-V mitting the necessary reciprocating component of the tool-holder motion. In that case the afore- The free end v of a VVtape-holder 8.

mentioned driving means drives the tool-holder table, while the iiexible tapes are connected to the tool-holder standard.

In order to'enable the invention to be readily carried into effect and the foregoing andV other features thereof tobe explained, a few embodiments will now be described by way of example with reference to the accompanying drawings, wherein:

Fig. 1 is a side elevation of a form of gear grinding machine embodying the invention, certain parts being shown broken away and others in section for greater clarity;

Fig. 2 is a top plan of the machine of Fig. l, with parts broken away;

Fig. 3 shows a detail of the machine on an enlarged scale, namely the involute-generating cylinder and the steel tapes and associated parts, a View of the grinding wheels being superposed thereon to explain the action;

Fig. 4 is a part-sectional rear elevation of the lower portion of the machine, showing the driving 'means for imparting the rolling motion to the "toolfholden Fig. vshows a detail of Fig. 4 on an enlarged scale; namely means for automatically obtaining periodic reversal of the rolling motion;

Fig, 6 isa tcp planV of the detail shown in Fig. 5;

Figs. 7 and 8 show another embodiment, according to the invention, of the driving means for imparting Vthe rolling motion to the tool-holder, both figures being vfragmentary views of portions at the rear of the machine, and Fig. '7 being a top plan, while Fig. Bis a part-sectional elevation of a` detail along the section line VIH-VIII mg.. i.: r Y Fig. 9 is a part-sectional top plan, similar to Fig. '7 showing yet another embodiment of the d rivingmeans as a Variant of that shown in Figs. 7and8.

lIn the form shown in Figs. l- G of the drawings, the machine comprises a bed I to which is secured an arm Zcarryinga stationary member 3 which is Va segment of a cylinder and constitutes the involutegenerating cylinder of the machine. Concentric ,with the vertical axis A of the involutegenerating cylinder 3,. is avcircular Work table 4 adapted to receive thegear wheel to be ground,

the ,work table 4 being mounted for rotation on r thepmachine bed {,but only for dividing or indexing purposes, and not for the purpose of the in- 'volute-generating rolling motion in which neither it nor the work 5 takes any part. When the grindling o fuone tooth` flankof the gear wheel 5 has beencompleteda dividing device of known type A(not s hown)Y rotates the work table 4 through an angle orrespondingvto one tooth pitch of the gear wheel 5 so that the latter presents the next 'tooth to the tool for grinding.

' Fastened to the cylindrical surface of the in- 'volute-generating cylinder 3 and passing partly around it in opposite directions are iiexible steel tapes 6, best seen in Fig., 3, the other ends of which pass partly around, and are secured to, rollers rEhe rollers 'I can be adjustedto place the tapes. 6 under high tension so that thev free portions of the .tapes lie in a plane which Ais tangential -to' the inVolute-generating v'cylinder 3. `Thetape-holder 8 is rigidly connected nto-astandard ,9 (Fig. 1) forming part of the toolholder of the machine. The standard 9 Yhas a slide IG mounted thereonfor vertical movement with respect thereto, for which purpose the standard 34 and the slide I3 are provided with suitable 4 cooperating guideways. The slide I0 has mounted thereon two further slides II, each carrying a grinding wheel I2 and each being adjustable with respect to the slide IIJ for the purpose of bringing the grinding wheel into proper operative engagement with the work. Ascan be seen from Fig. 3, the two grinding wheels are adaptedv to be set at an angle to each other so that their active surfaces are in operative engagement with opposed flanks of adjacent teeth of the work for grinding these two flanks simultaneously. In the present embodiment, each of the grinding wheels l2 is adapted to be set so that its active surface forms an angle with a line tangential to the involutegenerating cylinder 3 equal to 90 minus the pressure angle of the gear being ground. The diameter of the involute-generating cylinder 3 is therefore equal to the pitch circle diameter of the gear being ground. If the grinding wheels were setv with their active surfaces at right angles to the tangent of the involute-generating cylinder, the diameter of the latter would of course be made equal to the base circle diameter of the gear being ground. It will be understood'of course, that while it is advantageous to provide two grinding wheels a single one would be suflicient.

The tool-holder also comprises a slide I3 and a table I4. The standard 3 is mounted upon the slide I3, and the latter in turn upon the table ifi which has an arm I5 pivotally connected to a stationary shaft or pivot I6 coaxial with the Yjoint axis A of the involute-generating cylinder 3 and the work 5. In this way the table I4 can be ro tated in an oscillating manner' in a horizontal plane about the axis A by means presently to be described. This rotation ofthe table Ili'takes place over part-circular guideways I 'I provided' on the machine bed I upon'which the table I is thus slidably mounted. The slide I3, together with, the standard 9 carried by it, can be adjusted towards and away from the axis A by means of guideways Illa provided on the table' iii, for the purpose of bringing the standard 3, and with it the tapes 6, into proper position in relation to the involute-generating cylinder 3. The rectilinear component of the rolling motion of the tool-holder relatively to the work is obtained by movement of the standard 9 along the siide 3' in a direction tangential to the involute-generat ing cylinder 3, for which purpose the standard il is guided by rollers I8 engaging between cooperating'portions cf the slide I3.-

The present invention is more particularly directed to the means for bringing about the 'rotary V movement of the table Id about the axis A. in

the present embodiment this is effected by means of a nut I9 pivotally connected to a bracket on the outer edge of the table Iii at lthe rear of the machine byv a vertical pivotpin 2i! (Figs. l and 2), the nut I3 being engaged by a motor-driven screw-threaded spindle 2| (Figs.`2 and e) Referring now particularly to Fig. 4, it will be seen that the `'spindle 2! isdriven by a pair of

bevel wheels

22 and 23 vhcusedin a cage Zfiln which the `spindle 2l is journalled. The bevel wheel 23 is secured on, and driven by, a shaft 25 which exr tends perpendicularly to the spindle 2! andparal,w lel .to the axis A and which has its bearings in a casing 2S secured to the machine bed i and is driven byan electric motor 21 via a worm gearing 28. The cage 24, Itogether with vlthe spindle 2.! and the bevel wheel `22, .is mounted for pivotal movement about the vbevelw'heel shaft A2&3. The

free end'of the spindlell is provided with a ring 23 'mounted on its tip by means of ball bear- .ings and adapted vto :roll'upon a bearing surface formed on a bracket 30 projecting from the table .I 4.

.As has been ,hcreinbefore indicated, the rotary component of the rolling vmotion of the tool-holder relatively to the work is in the nature of oscillations, the tool-holder rotating back and forth through a predetermined comparatively small arc, and it follows that the rotation of the table I4 must be a to-and-fro oscillation, means being Aprovided to reverse its rotation when it has reached the end of the predetermined arc. In the present embodiment, this is effected by automatically reversing the motor 27 each time when the table I4 has traversed its arc of rotation about -the axis A. For this purpose, the bevel wheel shaft carries at its upper end a pinion .'SI (Figs. 5 and 6) driving, by engagement with a gear wheel 32 and associated pinion 33, a larger wheel 34. Mounted coaxially with the latter are two trip arms 35 each of which is provided with a handle 36 by means of which it can be manually adjusted to a desired angular position with respect to the axis of the gear wheel .34, In order to do so, the handle 36 is pulled upwardly against the pressure" of a spring, whereupon it can be rotated thereby causing a pinion 31 .meshing with the upper part of the gear wheel 34 to run along the teeth of the latter and thus to turn the trip arm 35 about the axis of the gear wheel 34. When the trip arm is in the desired position, thehandle 36 is released and is pulied downwardly by the spring, whereby dog-clutch teeth 38 on the handle 36 and the trip arm 35 are engaged with each other, thus locking the handle 38, and with it the pinion 37, against further rotation relatively to the gear wheel 34, so that the trip arm is then constrained to rotate with the gear wheel 34. As will now be appreciated, the initial upward pull on the handle before adjustment of the trip arm 35 is necessary in order to disengage the dog-clutch teeth 33 from each other so as to free the pinion 3i for rotation. These adjusting and locking arrangements are of course provided for each of the two trip arms 35 and adjustment is effected with the shaft and the gear wheel 34 stationary. `When the latter are subsequently driven in one direction, one of the arms is adapted to strike a switch arm 39 of a switch 49 which switch arm extends into the path of the two trip arms. The switch 40 has been diagrammatically shown in Fig. 6 and is soy arranged that, when actuated by the switch arm 39 being struck by either trip arm 35 and so moved in either direction, it alters the connections of the electric circuit energising the motor 2 in such a manner as to change the direction of rotation of the latter but does not entirely cut it out, the motor being always left running in one direction or the other. Each reversal of the motor 21 of course affects the gear wheel 34 also, causing the trip arms 35 to rotate in the opposite direction. The fact of the pinion 3l engaging only the upper part of the gear wheel 34 enables it, if necessary, to be moved past the driving pinion 33 which only engages the lower part of the gear wheel 34.

The operation of this form of gear grinding machine is as follows:

Before starting the machine up, the trip arms 35 are rst adjusted so as to enclose between them the desired angle O (Fig. 6) which ensures that the switch 40 is actuated to cause the table i4 to oscillate about axis A through an arc subtending an angle (Fig. 2'), the latter being. vso

chosen that :each of the two grinding wheels I2 `near the base circle level to the tip of the tooth.

The motor 21 is vthen vstarted up and, in conjunction with the reversing switch mechanism described inthe foregoing, causes the table I4 to be slowly swung to and fro about the axis A through the angle the broken lines in Fig. 2 indicating the table in the position at the end of the are of traverse in one direction. This movement of the table I4 'also causes the nut I9 bodily to make a small movement in an arc of a circle, the nut IS in turn rocking the spindle 2I aboutthe bevel wheel shaft 25 through a small angle, while the tip of the spindle 2| rolls along the bearing surface 33, the necessary rotation of the nut I 9 relatively to the table I4 being allowed for by the pivot 23. As the standard 9 is coupled by the tapes 6 to the stationary involutegenerating cylinder 3, it is unable entirely to 'follow the rotary swinging movement of the table I4, since this would involve both rollers 'I making a circular movement about the axis A which the tapes will clearly not permit. Instead, the standard 9, while being swung round on the table I4, is forced by the tapes 6 to reciprocate laterally across the table I4 by being displaced relatively to the slide I3 along the guides i8. It will be appreciated that this reciprocating movement takes place tangentially of the involute-gen'erating cylinder 3 and that it constitutes the reciprocating component of movement of the tool holder which 'combines 'with the rotary component imparted to the standard 9 by the table I4 ot provide the necessary true rolling motion of the tool-holder through an angle equal to =2a, so that each grinding wheel I2 rolls through the desired angle a (Fig. 2) with its active surface describing an involute profile.

While the rolling motion of the grinding wheels I2 as described in the foregoing is taking place comparatively slowly, the slide ID carrying the grinding wheels is moved rapidly up and down along the standard 9 by known poweropera-ted means which have not been shown in the drawings as they are not relevant to the present invention. This results in the grinding wheels moving along 'the whole length of the teeth, i. e. along the whole width of the gear wheel 5, which of course is stationary at this time, so that duringsuccessive strokes of the slide I8 each of the two tooth nan-ks with which I .ment of the table I4 are interrupted (by known means which it is not necessary to describe or show herein) for a period just long enough to ena-bie the work table 4 to be rotated by the dividing device already referred to so as to turn the gear wheel 5 by one tooth pitch and present two other tooth iianks toA the grinding wheels, whereupon the movement of the slide I 0 and the 7 table I4 are resumed and the operation is repeated. I l

In the embodiment described in the foregoing, in order to permit the rotary motion of the table I4 notwithstanding its connection to the spindle 2| by means of the pivoted nut I9 and the rectilinear motion of the latter on the formerl thespindle 2| is adapted for pivotal movement in a horizontal plane about the axis of the bevel wheel shaft 25,the opposite end of the spindle being free to swing towards and away from the table I4. In the two embodiments according to Figs. 7 to 9, the same result is achieved with the spindle 2| having both its ends supported so that the spindle has no bodily movement relatively to the machine bed I, while the pivoted nut I9 is so mounted on the table I4 that the latter can move towards and away from the nut I9. Two examples of how this may be carried into practical eect are shown in Figs. 7 and 8 and Fig. 9 respectively. It may be assumed that in both these embodiments, the remainder of 4the machine is substantially the same as in Figs. 1-5, including the means for automatically obtaining reversal of the swinging motion of the table I4 Y at either end of its oscillating motion through the arc for which it has been adjusted.

Referring rst to Figs. 7 and 8, the spindle 2 I, again driven through

bevel wheels

22, 23 by the shaft 25,Y is in this case journalled directly in the casing 26 xed to the machine bed I, the cage 24 being omitted as unnecessary. The opposite end ofV the spindle 2I is journalled in a bearing bracket 4I on the bed I. The nut I9 engaging the spindle is again mounted for pivotal movement withV respect to the table I4 about a vertical axis, and inV addition it is slidable towardsand away from the table I4. For this purpose the nut I9 has two pivot pins 20 projecting respectively from the tcp and bottom thereof in opposite directions. The pivot pins are rotatably as well as slidably mounted in a guideway 42 provided by slots in a forked bracket 43 on the table I4. The bracket 43 receives the nut I9 movably between its top and bottom prongs. Each of the pivot pins 20 is surrounded by a ball-bearing ring 44, by means of which the pins 2i! engage the guideway 42. The distance between the opposed guide faces of the guideway 42 is slightly larger than the outside diameter of the ball-bearing rings 44, so that the latter, in operation, engage the guideway 42 on one side thereof only, for reasons which will be readily apparent. The ball-bearing rings 44 are held in position by members 45 screwed to the top and bottom respectively of the two pivot pins. For greater clarity the members 45 have been omitted in Fig. '7.

In operation, as the nut I9 courses along the spindle 2|, the ball-bearings 44 roll along the guide faces of the guideways 42, the table I4 thus being free toassume different angular positions with respect to the nut I9, because the bracket 43 pivots about the nut I9 and slides alongit radially with respect to the axis of oscillation A of the table I4.

Fig. 9 shows a modification of the embodiment according to Figs. 7 and 8, the only change being in regard to the mounting of the nut I9 on the table I4 whilst the drive and mounting of the spindle 2I are the same as in Figs. '7 and 8. The nut I9, its pivot pins 20 and ball-bearings 44 are also constructed as in Figs. '7 and 8, but in the present embodiment the ball-bearings 44 are engaged in the end of a lever 41 pivoted at 48 to a 8 forked bracket 49 on the table I4." As' will' be readily apparent, the operation of this embodiment is analogous to that of Figs. 7 and 8, in that the lever 41, during the travel of the nut I9 along the spindle 2I, makes small pivotal movements about the pivots 20 and 48, thus allowing relative movement of the table I4 and the nut I9 towards and away from each other and permitting the former to take up different angular positions with respect to the latter.

What I claim and desire to secure by Letters Patent is:

1. In a gear grinding machine, the combination of a machine bed, a normally stationary work table mounted on said bed, a stationary involute-generating cylinder coaxial with said work table, a tool-holder, at least one grinding wheel carried by said tool-holder, said tool-holder being mounted on said bed for rotary movement about the axis of, and for rectilinear sliding movement tangentially of, said cylinder, and iiexible tapes coupling said tool-holder to said cylinder for constraining said tool-holder to perform a combination of both said movements and causing an involute-generating motion of said grinding wheel relatively to the work, with driving means for imparting said rotary movement to said tool-holder comprising a power-driven shaft mounted in fixed relation to said bed and extending parallel to said cylinder axis, a screw-threaded spindle coupled to said shaft for being driven thereby, a nut engaging said spindle and having pivotal connection with said tool-holder, means between said shaft and said tool-holder for permitting said rotary movement of said tool-holder relatively to said shaft notwithstanding the driving connection therebetween by said spindle and said nut, a reversible electric motor coupled to said shaft for driving same, switch means electrically connected in the energizing circuit of said motor for reversing the latter, a control device including rotatable means driven by said shaft and operatively associated with said switch means for periodically actuating said switch means to cause reversal of said motor and of said shaft and said spindle, and means for adjusting the operative relation of said rotatable means to said switch means to vary the angle of said rotary movement of said tool-holder.

2. In a gear grinding machine, the combination of a machine bed, a normally stationary work table mounted on said bed, a stationary involute-generating cylinder coaxial with said work table, a tool-holder including a vtable mounted on said bed for rotary oscillating movement about the axis of said cylinder and a standard mounted on said tool-holder table for rectilinear reciprocating movement relatively thereto tangentially of said cylinder, at least one grinding wheel carried by said tool-holder standard for reeiproeaticn relatively thereto parallel to said cylinder axis, and flexible tapes coupling said tool-holder standard to said Acylinder for constraining said tool-holder standardV to make said reciprocating movement when said toolholder table makes said rotaryoscillating movement for resultant involute-gene'rating motion of said grinding wheel, with driving means for imparting said rotary oscillating movement to said tool-holder table, comprising a power-driven screw-threaded spindle, a nut pivotally connected to said tool-holder tableand engaging said spindle intermediate its ends, means for supporting said spindle adjacent'one end thereof for rotation and for bodily pivotal movement thereof about an axis parallel to said cylinder axis, a pair of bevel wheels for driving said spindle, and a power-driven shaft extending parallel to the axis of said cylinder and having one of said bevel wheels secured thereon, and said spindle supporting means comprising a bearing member mounted for pivotal movement upon said shaft and having said spindle rotatably journaled therein, said shaft thus providing4 said axis of said bodily pivotal movement of said spindle.

3. In a gear grinding machine, the combination of a machine'bed, a normally stationary Work table mounted on said bed, a stationary involute-generating cylinder coaxial with said work table, a tool-holder including a table mounted on said bed for rotary oscillating movement about the axis of said cylinder and a standard mounted on said tool-holder table for rectilinear reciprocating movement relatively thereto tangentially of said cylinder', at least one grinding wheel carried by said tool-holder standard for reciprocation relatively thereto parallel to said cylinder axis, and lflexible tapes coupling said tool-holder standard to said cylinder for constraining said tool-holder standard to make said reciprocating movement when said toolholder table makes said rotary oscillating movement for resultant involute-generating motion of said grinding wheel, .with driving means for imparting said rotary oscillating movement to said tool-holder table comprising a power-driven screw-threaded spindle, a nut pivotally connected to said tool-holder table and engaging said spindle intermediate its ends, means for supporting said spindle adjacent one end thereof for rotation and for bodily pivotal movement thereof about an axis parallel to said cylinder axis, and means for slidably supporting the other end of said spindle.

4. The combination claimed in claim 3, said means for slidably supporting said other spindle end comprising a plane bearing surface provided on said tool-holder table, and a ring member mounted on said other spindle end for rotation relatively thereto and for rolling movement upon said bearing surface.

5. In a gear grinding machine, the combination of a machine bed, a normally stationary work table mounted on said bed, a stationary involute-generating cylinder coaxial with said work table, a tool-holder including a table mounted on said bed for rotary oscillating movement about the axis of said cylinder and a standard mounted on said tool-holder table for rectilinear reciprocating movement relatively thereto tangentially of said cylinder, at least one grinding Wheel carried by said tool-holder standard for reciprocation relatively thereto parallel to said cylinder axis, and flexible tapes coupling said tool-holder standard to said cylinder for constraining said tool-holder standard to make said reciprocating movement when said toolholder table makes said rotary oscillating movement for resultant involute-generating motion of said grinding wheel, with driving means for imparting said rotary oscillating movement to said tool-holder table, said driving means comprising a power-driven screw-threaded spindle mounted on said bed for rotation but not for bodily movement relative thereto, a nut engaging said spindle, means pivotally connecting said nut to said tool-holder table, cooperating guide means on said pivot means and said toolholder table respectively for permitting relative bodily movement between said nut and said toolholder table in adirection towardsv and away from said cylinder axis, said pivotal connecting means consisting of pivot means projecting from said nut and ysaid cooperating guide means being annular and rotatably mounted on said pvot means and a forked bracket projecting from said tool-holder table and having guide surfaces for rolling engagement by said annular guide means and for sliding engagement by said nut to prevent rotation of the nut with said spindle.

6. In a gear grinding machine, the combination of a machine bed, a normally stationary work table mounted on said bed, a stationary involute-generating cylinder coaxial with said work table, a tool-holder including a table mounted on said bed for rotary oscillating movement about the axis of said, cylinder and a standard mounted on said tool-holder table for rectilinear reciprocating movement relatively thereto tangentially of said cylinder, at least one grinding wheel carried by said tool-holder standard for reciprocation relatively thereto parallel to said cylinder axis, and exible tapes coupling said tool-holder Vstandard to said cylinder for constraining said tool-holder standard to make saidY reciprocating movement when said -toolholderrtable makes said rotary oscillating movement for resultant involute-generating motion of said grinding wheel, with driving means for imparting said rotary oscillating movement to said tool-holder table, said driving means comprising a power-driven screw-threaded spindle mounted on said bed for rotation but not for bodily movement relatively thereto, a nut engaging said spindle, and a lever having said nut pivotally mounted thereon and being pivotally connected to said tool-holder table for permitting relative bodily movement between said nut and said tool-holder table in a direction towards and away from said cylinder axis.

7. In a gear grinding machine, in combination, a machine bed, a normally stationary work table mounted on said bed, a stationary involute-generating cylinder coaxial with said work table, a tool-holder including a table mounted on said bed for rotary oscillating movement about the axis of said cylinder and a standard mounted on said tool-holder table for rectilinear reciprocating movement relatively thereto tangentially of said cylinder, at least one grinding wheel carried by said tool-holder standard for reciprocation relatively thereto parallel to said cylinder axis, and flexible tapes coupling said tool-holder standard to said cylinder for constraining said tool-holder standard to make said reciprocating movement when said tool-holder table makes said rotary oscillating movement for resultant involute-generating motion of said grinding wheel, driving means for imparting said rotary oscillating movement to said tool-holder table, said driving means including a power-driven shaft mounted on said bed for rotation but not for bodily movement relatively thereto and extending parallel to said cylinder axis, a rotatable screw-threaded spindle coupled to said shaft for being driven thereby, a nut engaging said spindle and having pivotal connection with said toolholder table, and means between said shaft and said tool-holder table for permitting said rotary oscillating movement of said tool-holder table relatively to said shaft notwithstanding the driving connection therebetween by said spindle and said nut, a control device operated by said driving means for periodically causing reversal of the rotation-of said shaft and said spindle, and means for adjusting said control device to cause said reversal after said tool-holder table has been moved through a predetermined angle of said rotary oscillating movementI thereof.

8. The combination claimed in claim 7, said driving means further including a reversible electric motor coupled to said shaft for driving the same, and said control device comprising a switch electrically connected in the energising circuit of said motor for reversing the latter, a switch arm for actuating said switch, a pair of trip arms coaxially mounted for joint rotation and coupled to said shaft to be rotated thereby, said trip arms projecting into the path of said switch arm for striking the latter and thereby actuating said switch to cause reversal of said motor and, hence, of the rotation of said shaft and said spindle, and means for adjusting the angle enclosed between said trip arms and the positions thereof relative to said switch arm for determining the angle of said oscillating rotary movement of said tool-holder table.

9. The combination claimed in claim 8, said adjusting means comprising a gear wheel for driving said trip arms and having said trip arms mounted thereon coaxially therewith, a manually operable member rotatably mounted on each of said trip arms for axial reciprocation relatively thereto between two positions, a pin- 12 ion secured to each of saidmanually operable members and extending therefrom into gearing engagement with said gear wheel, spring means associated with each ofV Asaid manually operable members for biasing it to one of said positions, clutch means associated with each of said manually operable members and effective, in Said biased position of said manually operable member, for locking it and said pinion against rotation on said trip arm to couple said trip arm to said gear wheel for joint rotation therewith, said clutch means being rendered ineiective upon manual reciprocation of said manually operable member to the other of said positions to permit said rotation of said manually operable member and said pinion for angular adjustment of said A trip arm relatively to said gear wheel.

HERMANN BUHLER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 903,106 Phelps Nov. 3, 1908 1,668,932 Aeppli May 8, 1928 FOREIGNv PATENTS Number Country Date 570,940 Great Britain July 30, 1945